g crosby



M. G, CROSBY RECEIVER WITH AUTOMATIC FREQUENCY-CONTROL Original Filed Nov. 2, 1955 Q ATTORNEY Sept. 12, 1939.

Patented Sept. 12, 1939 UNiTED STA'ii CONTR Riverhead, N. Y., assignor to Murray G. Crosby,

Radio Corporation of America, a corporation of Delaware Original application November 2, 1935, Serial No.

47,933, now Patent No. 2,085,008, dated .lune 29,

1937. Divided and this application April 21, 1937, Serial No. 138,117

13 Claims. (Cl. Z50- 20) My present invention is a division of my copending application Serial No. 47,933, filed November 2, 1935 and granted June 29, 1937 as Patent No. 2,085,008. Figures 1 and 2 of the present application correspond to Figures 8 and 8A of my parent application.

The object of my present invention is to provide an improved receiving system particularly adapted for the reception oi phase modulated waves.

Figure l is a wiring diagram of my improved receiver and Figure 2 is a graph explanatory of the operation of the frequency control system. of Figure 1.

The circuit of the drawing shows a phase modulation receiver utilizing the principles of this disclosure wherein the shielded type of crystal filter is employed. The phase modulated intermediate frequency energy is fed from I to the control grid and cathode of tube 52 and to coupling tube 5l and from the anode of 5l to the tuned circuit 56 connected with said anode. This tuned circuit 5B has the input electrodes of the shielded crystal filter 53 across it and the tuned circuit 56 is normally tuned so as to tune out the capacity of the crystal holder. This tuning will allow the crystal to produce a dip point in the resonance curve of the tuned circuit so that the combined resonant characteristic is as shown in Figure 2 of the drawing wherein Fc is the mean or carrier wave frequency. On either side of this dip point, the phase of the voltage across the tuned circuit and crystal will change very rapidly due tothe high selectivity of the crystal. Thus, filtered energy, the phase of which changes very rapidly with frequency and the amplitude of which increases very rapidly as the resonance point of the crystal is deviated from, is available for the automatic frequency control diode detectors 54 and 55. Such a crystal filter produces an ideal characteristic for automatic frequency control purposes, since the farther off tune the signal is, the greater the energy is which is available to correct the tuning, This filtered energy is combined with the unltered energy from coupling tube 52 by feeding it to the midtap of push-pull input transformer 58, the primary winding of which is connected to the anode of 52. The automatic frequency control energy is taken from the resistors of diode detectors 55 and 55 and passed to the modulator tube 59 which controls the frequency of the rst or second superheterodyne oscillator. The energy which is fed to` the audio frequency amplifying diode 5l for `the detection of the signal is converted from phase modulation to amplitude modulation by means of the three-electrode crystal filter, as in the prior modification. Such a crystal iilter may have a shield S between its input and output electrodes, as shown in Figure l by dotted lines, butin this circuit a capacity C is provided to destroy the shielding and convert the filter fromv a symmetrical characteristic filter, as shown in Figure l of my above referred to patent, to an unsymmetrical characteristic lter, as shown in Figure 2 ci my above referred to patent, as to the energy fed to the detector 5l. This capacity might be replaced by some sort of a variable shielding means also; for instance, a movable grounded plate could be slid between the two electrodes to variably shield them from each other.

In Figure l, the ltered energy is impressed in like phase on the diode input electrodes, while the unfiltered energy is applied in phase displaced relation on these electrodes. The proper phase quadrature" relation may be produced by adjusting the tune of 62.

When only a single crystal iilter' is used, as for phase modulation reception, amplitude modulation comes through to a certain extent due tothe single sideband action of the crystal filter. Since the sidebands on one side of the carrier are eliminated due to the dip point in the unneutralized filter characteristic, the filter acts as a single sideband lter for the lower modulation frequencies. Thus, the lower modulation frequencies of either phase cr amplitude modulation will come through on the phase modulation adjustment.

The principles utilized in this disclosure are not limited to the use of crystal filters. Thus, any mechanical lilter or artificial line type of circuit may be used. The fundamental'requisite is that the phase be shifted either capacitive on both sides of the resonant frequency or inductive on both sides of the resonant frequency. The required efiect is the shift of the carrier in phase with respect to the sidebands or vice versa. The fundamental circuit of Figure 5 of my parent application has other equivalent circuits which will perform the same function.

If desired, an audio frequency amplifier or telephones T or loudspeaker may be connected directly across the resistors 65, 58. When doing this, the diode detector 5l and its associated circuit elements within the rectangle R may be dispensed with.

Having thus described my invention, what I claim is:

l. 1n a demodulator system for demodulating a wave the phase of which has been modulated in accordance with intelligence, an alternating current circuit, a source of local oscillations of variable frequency coupled to said circuit, demodulating means coupled to said circuit, an intermediate frequency amplifier coupled to said demodulating means, a coupling tube having a control grid coupled to said intermediate frequency amplier, said tube having an anode electrode, a tuned circuit coupled to the anode of said tube, a piezo-electric crystal connected in shunt to said tuned circuit, a pair of differential detectors, a circuit connecting the input of said diiferential detectors to the anode of said last named tube, a second tube having its control grid coupled to said intermediate frequency amplifier, a circuit coupling the anode of said last named tube to said differential detectors, and a circuit coupling said differential detectors to said oscillator of variable frequency.

2. A system as recited in claim 1 wherein a utilization circuit is coupled to said crystal.

3. A phase modulated wave receiver comprising a crystal having a plurality of pairs of electrodes, a circuit connected across a pair of said electrodes, means for applying received phase modulated energy to said circuit connected across said pair of electrodes, a second circuit connected across another pair of said electrodes, means for detecting the energy appearing in said second circuit, and means reactively coupling said circuits together.

4. Apparatus as claimed in claim 3, characterized by the fact that said coupling means is capacitive,

5. Apparatus as claimed in claim 3, characterized by the fact that said coupling means comprises a variable condenser.

6. In a receiving system, a crystal having a grounded electrode and two auxiliary electrodes, means for applying received Wave energy across said grounded electrode and one of said auxiliary electrodes, means for deriving a voltage from said grounded electrode and the other auxiliary electrode, means for detecting the derived voltage, and means for variably coupling together said auxiliary electrodes.

'7. In a receiver, a parallel resonant circuit, means for feeding received energy to said parallel resonant circuit, a crystal having electrodes Connected in shunt to a portion of said parallel circuit, said crystal being resonant at substantially the mean frequency of said received energy, said parallel circuit being tuned to substantially tune out the capacity between said crystal electrodes, means combining received energy and energy from said tuned circuit in phase quadrature, means for detecting the combined energies. a local oscillation generator, and means responsive to the detected energies to control the frequency of said local oscillation generator.

8. Apparatus as recited in claim 7, characterized by the fact that a detector is coupled to said crystal for reproducing the transmitted signal.

9. A receiver comprising means for receiving waves, a local oscillator, means for combining local oscillations with the received waves so as to produce beat frequency oscillations, a tuned circuit exhibiting parallel resonance effects, means for applying the beat frequency Waves to said tuned circuit, a crystal having pairs of electrodes with one pair connected in shunt to said tuned circuit, means combining waves of all beat frequencies and waves from said tuned circuit in phase displaced relationship, means for detecting said combined waves, and means responsive to the detected Waves to vary the frequency of said local oscillator.

10. Apparatus as recited in claim 9, characterized by the provision of circuits, including a detector, coupled to a pair of electrodes of said crystal for reproducing a transmitted signal.

1l. Apparatus as claimed in claim 9, characterized by the fact that the received waves are phase modulated waves, and also characterized by the fact that circuits including a detector are coupled to a pair of said crystal electrodes for reproducing a transmitted signal, and being further characterized by the fact that a reactive circuit is connected effectively in shunt to a pair of electrodes of said crystal whereby said crystal and shunt circuit effectively transform the phase modulated intermediate frequency waves into amplitude modulated waves prior to detection.

12. A system as recited in claim 1 wherein signal frequency indicating means is coupled to said differential detectors to reproduce the transmitted signal.

13. A receiver as recited in claim 9 wherein signal indicating means is connected to said means for detecting said combined Waves for reproducing the transmitted signal.

MURRAY G. CROSBY. 

